Optical device and manufacturing method therefor

ABSTRACT

An optical device including a substrate formed of a light transmitting material and a light emitting layer formed on the front surface of the substrate. Both the front surface and the back surface of the substrate are parallel to each other and have substantially the same rectangular shape. The substrate has four side surfaces connecting the front surface and the back surface of the substrate. Each side surface of the substrate has a corrugated sectional shape such that a plurality of concave portions and convex portions are alternately formed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical device composed of asubstrate and a light emitting layer formed on the front surface of thesubstrate and also to a manufacturing method for the optical device.

2. Description of the Related Art

In a fabrication process for an optical device such as a laser diode(LD) and a light emitting diode (LED), a light emitting layer (epitaxiallayer) is formed by epitaxial growth, for example, on the upper surface(front surface) of a crystal growing substrate of sapphire, SiC, or thelike, thereby manufacturing an optical device wafer for forming aplurality of optical devices. The light emitting layer formed on thecrystal growing substrate of the optical device wafer is partitioned bya plurality of crossing division lines to define a plurality of separateregions where the plural optical devices such as LDs and LEDs arerespectively formed. The optical device wafer is divided along thesedivision lines to obtain the individual optical devices as chips.

As a method of dividing the optical device wafer along the divisionlines, there are known methods as described in Japanese Patent Laid-openNos. Hei 10-305420 and 2008-006492. The dividing method described inJapanese Patent Laid-open No. Hei 10-305420 includes the steps ofapplying a pulsed laser beam having an absorption wavelength to thewafer along the division lines to form a laser processed groove alongeach division line by ablation and next applying an external force tothe wafer to thereby break the wafer along each division line where thelaser processed groove is formed as a division start point.

On the other hand, the dividing method described in Japanese PatentLaid-open No. 2008-006492 is intended to improve the luminance of theoptical device and it includes the steps of applying a pulsed laser beamhaving a transmission wavelength to the wafer along the division linesin the condition where the focal point of the pulsed laser beam is setinside the wafer, thereby forming a modified layer inside the waferalong each division line and next applying an external force to eachdivision line where the modified layer is formed to be reduced instrength, thereby dividing the wafer along each division line.

SUMMARY OF THE INVENTION

In each of the dividing methods described in Japanese Patent Laid-openNos. Hei 10-305420 and 2008-006492, the laser beam is directed to theoptical device wafer substantially perpendicularly thereto to form thelaser processed groove or the modified layer and then divide the opticaldevice wafer along the laser processed groove or the modified layer as adivision start point, thereby obtaining the individual optical devices.Each optical device has a rectangular boxlike shape such that each sidesurface is substantially perpendicular to the light emitting layerformed on the front surface of the substrate. Accordingly, of the lightemitted from the light emitting layer of the optical device, theproportion of the light striking each side surface at an incident anglegreater than the critical angle is large. As a result, the proportion ofthe light totally reflected on each side surface is large, so that thereis a possibility that the light repeating the internal total reflectionin the substrate may finally become extinct in the substrate.Accordingly, the light extraction efficiency of the optical device isreduced to cause a reduction in luminance.

It is therefore an object of the present invention to provide an opticaldevice and a manufacturing method therefor which can improve the lightextraction efficiency.

In accordance with an aspect of the present invention, there is providedan optical device including: a substrate formed of a light transmittingmaterial; and a light emitting layer formed on the front surface of thesubstrate; both the front surface and the back surface of the substratebeing parallel to each other and having substantially the samerectangular shape; the substrate having four side surfaces connectingthe front surface and the back surface of the substrate; each sidesurface of the substrate having a corrugated sectional shape such that aplurality of concave portions and convex portions are alternatelyformed.

With this configuration, each side surface of the substrate of theoptical device has a corrugated sectional shape. Accordingly, of thelight emitted from the light emitting layer and striking each sidesurface, the proportion of the light striking each side surface at anincident angle less than or equal to the critical angle can beincreased. As a result, the proportion of the light totally reflected oneach side surface and returned to the light emitting layer can bereduced to thereby increase the proportion of the light emerging fromeach side surface. That is, the light extraction efficiency can beimproved. The corrugated sectional shape mentioned above is not limitedto such a shape that the concave portions and the convex portions havean arcuate shape or any curved shape, but includes an angular shape(sawtooth shape) such that the concave portions and the convex portionsare pointed.

In accordance with another aspect of the present invention, there isprovided a manufacturing method for optical devices each including asubstrate formed of a light transmitting material and a light emittinglayer formed on the front surface of the substrate, both the frontsurface and the back surface of the substrate being parallel to eachother and having substantially the same rectangular shape, the substratehaving four side surfaces connecting the front surface and the backsurface of the substrate, each side surface of the substrate having acorrugated sectional shape such that a plurality of concave portions andconvex portions are alternately formed, the manufacturing methodincluding: an attaching step of attaching a protective tape to the frontside of an optical device wafer having a light emitting layer on thefront side, the light emitting layer of the optical device wafer beingpartitioned by a plurality of crossing division lines to define aplurality of separate regions where the optical devices are respectivelyformed; a modified layer forming step of applying a laser beam having atransmission wavelength to the optical device wafer along each divisionline from the back side of the optical device wafer after performing theattaching step, in the condition where the focal point of the laser beamis adjusted inside the optical device wafer so as to be stepwise shiftedalong the thickness of the optical device wafer from the front side tothe back side thereof, thereby forming a plurality of modified layersjuxtaposed in the direction along the thickness of the optical devicewafer; and a dividing step of applying an external force to the opticaldevice wafer after performing the modified layer forming step, therebydividing the optical device wafer along each division line to obtain theindividual optical devices; the plurality of modified layers juxtaposedin the direction along the thickness of the optical device wafer beingstaggered in the direction along the width of each division line in themodified layer forming step; a crack being formed between any adjacentones of the plural modified layers juxtaposed along the thickness of theoptical device wafer and staggered along the width of each division linein the dividing step, thereby dividing the optical device wafer alongeach division line so as to form a corrugated sectional shapecorresponding to the shape of each side surface of the substrate of eachoptical device.

According to this method, the optical devices each having corrugatedside surfaces can be manufactured without complication of each step andelongation of the time of each step.

The above and other objects, features and advantages of the presentinvention and the manner of realizing them will become more apparent,and the invention itself will best be understood from a study of thefollowing description and appended claims with reference to the attacheddrawings showing a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of an optical device according toa preferred embodiment of the present invention;

FIG. 2 is a schematic sectional view for illustrating a manner ofemission of light from the optical device shown in FIG. 1;

FIG. 3 is a schematic sectional view for illustrating a manner ofemission of light from a conventional optical device as a comparison;

FIG. 4 is a perspective view of a laser processing apparatus to be usedin manufacturing the optical device shown in FIG. 1;

FIG. 5A is a sectional view for illustrating an attaching step;

FIG. 5B is a sectional view for illustrating a modified layer formingstep;

FIG. 5C is a sectional view for illustrating a dividing step;

FIG. 6A is a schematic perspective view of an optical device wafer;

FIG. 6B is a cross section taken along the line A-A in FIG. 6A forillustrating a condition before breaking the optical device wafer;

FIG. 6C is a view similar to FIG. 6B for illustrating a condition afterbreaking the optical device wafer;

FIG. 7A is an enlarged plan view for illustrating the modified layerforming step; and

FIG. 7B is a schematic cross section taken along the line B-B in FIG.7A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the optical device and the manufacturingmethod therefor according to the present invention will now be describedin detail with reference to the attached drawings. There will first bedescribed a preferred embodiment of the optical device according to thepresent invention with reference to FIGS. 1 and 2. FIG. 1 is a schematicperspective view of an optical device 1 according to this preferredembodiment, and FIG. 2 is a schematic sectional view for illustrating amanner of emission of light from the optical device 1 shown in FIG. 1.

As shown in FIGS. 1 and 2, the optical device 1 is adapted to be mountedon a base 11 (not shown in FIG. 1) by wire bonding or flip chip bonding.The optical device 1 is composed of a substrate 21 and a light emittinglayer 22 formed on the front surface 21 a of the substrate 21. Thesubstrate 21 is a crystal growing substrate selected from a sapphiresubstrate (Al₂O₃ substrate), gallium nitride substrate (GaN substrate),silicon carbide substrate (SiC substrate), and gallium oxide substrate(Ga₂O₃ substrate), for example. The substrate 21 is preferably formed ofa light transmitting material. More preferably, the substrate 21 isformed of a transparent material.

The light emitting layer 22 is formed by the epitaxial growth of ann-type semiconductor layer (e.g., n-type GaN layer) in which electronsfunction as majority carrier, a semiconductor layer (e.g., InGaN layer),and a p-type semiconductor layer (e.g., p-type GaN layer) in which holesfunction as majority carrier. These layers are epitaxially grown in thisorder on the front surface 21 a of the substrate 21. The light emittinglayer 22 is formed with two electrodes (not shown) respectivelyconnected to the n-type semiconductor layer and the p-type semiconductorlayer. A voltage from an external power source is applied to the twoelectrodes to thereby emit light from the light emitting layer 22.

Both the front surface 21 a and the back surface 21 b of the substrate21 have substantially the same rectangular shape as viewed in plan andthey are parallel to each other. The substrate 21 has four side surfaces21 c respectively connecting the four sides of the front surface 21 aand the four sides of the back surface 21 b. Each side surface 21 c hasa corrugated sectional shape as taken along the thickness of thesubstrate 21 such that a plurality of concave portions 25 and convexportions 26 are alternately formed along the thickness of the substrate21. In this preferred embodiment, each concave portion 25 and eachconvex portion 26 have a gently curved shape. However, the corrugatedsectional shape of each side surface 21 c is not limited to that shownin FIG. 2, but may include a sawtooth shape such that the concaveportions 25 and the convex portions 26 become pointed.

The luminance improving effect by the optical device 1 shown in FIG. 2will now be described in comparison with a conventional optical device 3shown in FIG. 3. FIG. 3 is a schematic sectional view for illustrating amanner of emission of light from the optical device 3 as a comparison.The optical device 3 shown in FIG. 3 is similar to the optical device 1shown in FIG. 2 except the shape of each side surface 21 c of thesubstrate 21. More specifically, the optical device 3 shown in FIG. 3 iscomposed of a substrate 31 and a light emitting layer 32 formed on thefront surface 31 a of the substrate 31. Both the front surface 31 a andthe back surface 31 b of the substrate 31 have substantially the samerectangular shape as viewed in plan. The optical device 3 is mounted ona base 33. The substrate 31 has four side surfaces 31 c, each of whichis a flat surface perpendicular to the front surface 31 a and the backsurface 31 b.

As shown in FIG. 2, the light generated in the light emitting layer 22of the optical device 1 according to this preferred embodiment isemitted mainly from the front surface 22 a and the back surface 22 b.The light emitted from the front surface 22 a of the light emittinglayer 22 (e.g., optical path A1) is extracted through a lens member (notshown) or the like to the outside. On the other hand, the light emittedfrom the back surface 22 b of the light emitting layer 22 andpropagating along an optical path A2 strikes the interface between theside surface 21 c of the substrate 21 and an air layer at an incidentangle θ1. Since the side surface 21 c is corrugated, the incidentsurface between the concave portion 25 and the convex portion 26adjacent to each other which the light propagating along the opticalpath A2 strikes is oriented (inclined) toward the light emitting layer22 as compared with a vertical flat surface. Accordingly, the incidentangle θ1 of the light propagating along the optical path A2 is so smallas to be less than or equal to the critical angle of the substrate 21.Accordingly, the light propagating along the optical path A2 ispartially transmitted through the side surface 21 c to the air layer(optical path A3), and the remaining light is reflected on the sidesurface 21 c (optical path A4).

The light propagating along the optical path A3 is next reflected on theupper surface of the base 11 and extracted to the outside. The lightpropagating along the optical path A4 travels in the substrate 21 in anearly horizontal direction as viewed in FIG. 2 because the incidentangle θ1 is small as mentioned above. The light thus traveling in thesubstrate 21 strikes the opposite side surface 21 c (right side surfaceas viewed in FIG. 2) and is next emerged to the air layer.

In contrast thereto, the light is emitted from the optical device 3 as acomparison shown in FIG. 3 to propagate along optical paths B1 and B2.The optical paths B1 and B2 of the light emitted from the optical device3 are similar to the optical paths A1 and A2 of the light emitted fromthe optical device 1. However, since the side surface 31 c of thesubstrate 31 is a flat surface perpendicular to the front surface 31 aand the back surface 31 b, the incident angle θ2 of the lightpropagating along the optical path B2 and striking the interface betweenthe side surface 31 c and the air layer is larger than the incidentangle θ1 shown in FIG. 2. Accordingly, the incident angle θ2 is largerthan the critical angle of the substrate 21, so that the lightpropagating along the optical path B2 is totally reflected on theinterface between the side surface 31 c and the air layer (optical pathB3). The light propagating along the optical path B3 is reflected on theupper surface of the base 33 (optical path B4). The light propagatingalong the optical path B4 travels in the substrate 31 in a nearlyvertical direction as viewed in FIG. 3 in comparison with the opticalpath A4. Accordingly, the light propagating along the optical path B4enters the light emitting layer 32 and is absorbed by the light emittinglayer 32, so that the light cannot be extracted to the outside.

According to the optical device 1 shown in FIG. 2, each side surface 21c of the substrate 21 is corrugated, so that the light emitted from thelight emitting layer 22 and propagating in the substrate 21 alongoptical paths similar to the optical path A2 can be extracted to theoutside along optical paths similar to the optical paths A3 and A4.Accordingly, as compared with the light propagating along optical pathssimilar to the optical path B2 shown in FIG. 3, the proportion of thelight totally reflected on each side surface 21 c to the lightpropagating along optical paths similar to the optical path A2 can bereduced. Accordingly, the proportion of the light repeating the internaltotal reflection in the substrate 21 and returning to the light emittinglayer 22 can be reduced and the proportion of the light emerging fromthe substrate 21 can be increased to thereby improve the lightextraction efficiency, resulting in the improvement in luminance.

There will now be described a preferred embodiment of the optical devicemanufacturing method according to the present invention. The opticaldevice manufacturing method in this preferred embodiment includes anattaching step, a modified layer forming step by a laser processingapparatus, and a dividing step by a dividing apparatus. In the attachingstep, an adhesive sheet (protective tape) is attached to the front sideof an optical device wafer on which a light emitting layer is formed. Inthe modified layer forming step, a plurality of modified layers areformed inside the optical device wafer along each division line. In thedividing step, the optical device wafer is divided along each divisionline where the modified layers are formed as a division start point,thereby obtaining a plurality of individual optical devices. These stepsof the manufacturing method will now be described in more detail.

Referring to FIG. 4, there is shown a perspective view of a laserprocessing apparatus 100 for forming the modified layers inside theoptical device wafer in this preferred embodiment. The configuration ofthe laser processing apparatus usable in the present invention is notlimited to that shown in FIG. 4. That is, any configuration capable offorming the modified layers inside the optical device wafer may beadopted as the laser processing apparatus.

As shown in FIG. 4, the laser processing apparatus 100 includes a laserprocessing unit 102 for applying a laser beam to an optical device waferW held on a chuck table (holding means) 103, wherein the laserprocessing unit 102 and the chuck table 103 are relatively moved toprocess the optical device wafer W. The laser processing apparatus 100has a boxlike base 101. There is provided on the upper surface of thebase 101 a chuck table moving mechanism 104 for feeding the chuck table103 in the X direction extending along an X axis shown in FIG. 4 andalso indexing the chuck table 103 in the Y direction extending along a Yaxis shown in FIG. 4. A wall portion 111 stands from the base 101 at itsrear end behind the chuck table moving mechanism 104. An arm portion 112projects from the front surface of the wall portion 111. The laserprocessing unit 102 is supported to the arm portion 112 so as to beopposed to the chuck table 103.

The chuck table moving mechanism 104 includes a pair of parallel guiderails 115 provided on the upper surface of the base 101 so as to extendin the X direction and a motor-driven X table 116 slidably supported tothe guide rails 115. The chuck table moving mechanism 104 furtherincludes a pair of parallel guide rails 117 provided on the uppersurface of the X table 116 so as to extend in the Y direction and amotor-driven Y table 118 slidably supported to the guide rails 117.

The chuck table 103 is provided on the upper surface of the Y table 118.Nut portions (not shown) are formed on the lower surfaces of the X table116 and the Y table 118, and ball screws 121 and 122 are threadedlyengaged with these nut portions of the X table 116 and the Y table 118,respectively. Drive motors 123 and 124 are connected to the end portionsof the ball screws 121 and 122, respectively. Accordingly, when the ballscrews 121 and 122 are rotationally driven by the drive motors 123 and124, respectively, the chuck table 103 is moved in the X direction andthe Y direction along the guide rails 115 and 117, respectively.

The chuck table 103 is a circular member and it is rotatably provided onthe upper surface of the Y table 118 through a θ table 125. A suctionholding member (not shown) of a porous ceramic material is formed on theupper surface of the chuck table 103. Four clamps 126 are provided onthe outer circumference of the chuck table 103, wherein each clamp 126is supported through a pair of arms to the chuck table 103. The fourclamps 126 are driven by an air actuator (not shown) to thereby fix aring frame F supporting the optical device wafer W through an adhesivesheet S in the condition where the wafer W is held on the chuck table103 under suction.

The laser processing unit 102 has a processing head 127 provided at thefront end of the arm portion 112. An optical system is provided in thearm portion 112 and the processing head 127 to constitute the laserprocessing unit 102. More specifically, a laser oscillator (not shown)is provided in the arm portion 112, and the processing head 127 includesa focusing lens (not shown) for focusing a laser beam oscillated fromthe laser oscillator to the optical device wafer W held on the chucktable 103, thereby processing the optical device wafer W. In this case,the laser beam has a transmission wavelength to the optical device waferW, and the focal point of the laser beam is adjusted by the opticalsystem so that the laser beam is focused inside the optical device waferW.

By the application of the laser beam to the optical device wafer W, aplurality of modified layers (reformed layers) R (see FIGS. 5B and 6B)as a division start point are formed inside the optical device wafer Walong each division line. Each modified layer R is a region differentfrom its ambient region in density, refractive index, mechanicalstrength, or any other physical properties in the optical device wafer Wirradiated with the laser beam. Examples of each modified layer Rinclude a melted region, cracked region, breakdown region, andrefractive index changed region. These regions may be mixed.

The optical device wafer W is a substantially disk-shaped member. Asshown in FIGS. 5A and 6A, the optical device wafer W is composed of asubstrate W1 and a light emitting layer W2 formed on the front side(upper surface as viewed in FIG. 5A) of the substrate W1. The lightemitting layer W2 of the optical device wafer W is partitioned by aplurality of crossing division lines (streets) ST to define a pluralityof separate regions where a plurality of optical devices 1 arerespectively formed. As shown in FIG. 4, the optical device wafer W tobe held on the chuck table 103 is attached to an adhesive sheet Ssupported to the ring frame F in the condition where the light emittinglayer W2 is oriented downward, i.e., the substrate W1 is orientedupward.

The optical device manufacturing method to be performed by processingthe optical device wafer W according to this preferred embodiment willnow be described with reference to FIGS. 5A to 7B. FIGS. 5A to 5C aresectional views for illustrating the steps of the optical devicemanufacturing method. FIG. 6A is a schematic perspective view of theoptical device wafer W and FIGS. 6B and 6C are cross sections takenalong the line A-A in FIG. 6A for illustrating different conditionsbefore and after breaking the optical device wafer W. FIG. 7A is anenlarged plan view for illustrating the modified layer forming step, andFIG. 7B is a schematic cross section taken along the line B-B in FIG.7A. The steps shown in FIGS. 5A to 5C are merely illustrative and thesteps of the optical device manufacturing method according to thepresent invention are not limited to those shown in FIGS. 5A to 5C.

The attaching step shown in FIG. 5A is first performed. As shown in FIG.5A, the optical device wafer W is positioned inside the ring frame F inthe condition where the light emitting layer W2 formed on the front sideof the substrate W1 is oriented upward. Thereafter, the front side(upper surface) of the optical device wafer W (i.e., the light emittinglayer W2) and the upper surface of the ring frame F are attached to theadhesive sheet S. Accordingly, the optical device wafer W is supportedthrough the adhesive sheet S to the ring frame F in the condition wherethe substrate W1 of the wafer W is exposed.

After performing the attaching step, the modified layer forming stepshown in FIG. 5B is performed. As shown in FIG. 5B, the optical devicewafer W supported through the adhesive sheet S to the ring frame F isheld on the chuck table 103 in the condition where the adhesive sheet Sis in contact with the upper surface of the chuck table 103 and the ringframe F is fixed by the clamps 126. Further, the lower end (laser beamoutlet) of the processing head 127 is positioned directly above apredetermined one of the division lines ST of the optical device waferW, and the laser beam is applied from the processing head 127 toward theback side of the optical device wafer W (i.e., the back side of thesubstrate W1). The wavelength of the laser beam is set to a transmissionwavelength to the optical device wafer W, and the focal point of thelaser beam is set inside the substrate W1 of the optical device wafer W.As adjusting the focal point of the laser beam, the chuck table 103holding the optical device wafer W is moved in the X direction and the Ydirection shown in FIG. 4 to thereby form the plural modified layers Rinside the optical device wafer W along each division line ST. As shownin FIG. 7A, each modified layer R along each division line ST iscomposed of plural spots arranged in a line with the pulse pitch Paccording to the wavelength of the laser beam. Further, as shown in FIG.7B which is a cross section taken along the line B-B in FIG. 7A, pluralvertical elongated ellipses are continuously arranged in a line to formeach modified layer R.

As shown in FIG. 6B, the plural modified layers R along each divisionline ST are formed by changing the vertical position of the focal pointof the laser beam along the thickness of the substrate W1. Morespecifically, the first modified layer R1 is formed by setting thevertical position of the focal point in FIG. 6B to a position above thefront side (lower surface as viewed in FIG. 6B) of the optical devicewafer W toward the back side (upper surface) thereof by a predeterminedamount and then applying the laser beam along the predetermined divisionline ST. The formation of the first modified layer R1 is repeated forall of the division lines ST. Thereafter, the focal point is shiftedupward by the predetermined amount to form the second modified layer R2along each division line ST. More specifically, the focal point is setat a position above the first modified layer R1 as horizontally shiftedtherefrom along the width of each division line ST by the index In (seeFIG. 7A). Thereafter, the third modified layer R3 is similarly formedabove the second modified layer R2 by shifting the focal point upward bythe predetermined amount and also shifting the focal point along thewidth of each division line ST by the index In. Thereafter, the fourthand fifth modified layers R4 and R5 are similarly formed as shown inFIG. 6B. Thusly, the plural modified layers R (the first to fifthmodified layers R1 to R5 in this preferred embodiment) are formed alongeach division line ST in such a manner that the plural modified layers Rare vertically juxtaposed from the front side (lower surface as viewedin FIG. 6B) of the optical device wafer W to the back side (uppersurface as viewed in FIG. 6B) thereof and horizontally staggered alongthe width of each division line ST. In this manner, the plural modifiedlayers R are formed as a division start point inside the optical devicewafer W along each division line ST.

After performing the modified layer forming step, the dividing stepshown in FIG. 5C is performed. As shown in FIG. 5C, the substrate W1 ofthe optical device wafer W is placed on a pair of parallel support beds35 constituting a breaking apparatus (not shown) in the condition thesubstrate W1 is oriented downward, and the ring frame F supporting theoptical device wafer W through the adhesive sheet S is placed on anannular table 36. The ring frame F placed on the annular table 36 isfixed by four clamps 37 provided on the annular table 36. The pair ofparallel support beds 35 extend in one direction (perpendicular to thesheet plane of FIG. 5C), and imaging means 38 is located between thesupport beds 35 on the lower side thereof. The imaging means 38functions to image the back side (lower surface as viewed in FIG. 5C) ofthe optical device wafer W, i.e., the back side of the substrate W1 frombetween the support beds 35.

A pressure blade 39 for pressing the optical device wafer W from theupper side thereof is provided above the support beds 35 at a horizontalposition therebetween. That is, an external force is applied from thepressure blade 39 to the optical device wafer W held on the support beds35. The pressure blade 39 extends in one direction (perpendicular to thesheet plane of FIG. 5C), and it is vertically movable by a pressureapplying mechanism (not shown). When the back side of the optical devicewafer W is imaged by the imaging means 38, a predetermined one of thedivision lines ST is positioned between the support beds 35 and directlybelow the pressure blade 39 according to an image obtained by theimaging means 38. Thereafter, the pressure blade 39 is lowered to abutagainst the optical device wafer W through the adhesive sheet S, therebyapplying an external force to the optical device wafer W to divide thewafer W along the predetermined division line ST where the pluralmodified layers R as a division start point are formed. At this time, acrack K (see FIG. 6C) is formed between any adjacent ones of the pluralmodified layers R juxtaposed along the thickness of the wafer W andstaggered along the width of the predetermined division line ST. By theformation of the crack K, the optical device wafer W is divided alongthe predetermined division line ST so as to form a corrugated sectionalshape corresponding to the shape of each side surface 21 c shown inFIGS. 1 and 2, i.e., the corrugated sectional shape composed of theplural concave portions 25 and the plural convex portions 26 alternatelyarranged. At this time, the plural modified layers R along thepredetermined division line ST form the concave portions 25 of one ofthe optical devices 1 adjacent to each other with the predetermineddivision line ST interposed therebetween, and simultaneously form theconvex portions 26 of the other optical device 1 (see FIGS. 6C and 7B).This dividing step is similarly performed along all of the divisionlines ST to thereby divide the optical device wafer W into theindividual optical devices 1.

Examples of the laser processing conditions in the modified layerforming step are shown below. The defocus amount in each exampleindicates the distance from the back side (upper surface as viewed inFIG. 5B) of the optical device wafer W to the focal point in thedirection along the thickness of the wafer W.

EXAMPLE 1

Power: 0.1 W

Work feed speed: 1000 mm/s

Index In: 6 μm

Number of modified layers R along each division line ST: 4

Defocus amount in forming the first modified layer R1: 40 μm

Defocus amount in forming the second modified layer R2: 32.5 μm

Defocus amount in forming the third modified layer R3: 25 μm

Defocus amount in forming the fourth modified layer R4: 17.5 μm

EXAMPLE 2

Power: 0.1 W

Work feed speed: 1000 mm/s

Index In: 6 μm

Number of modified layers R along each division line ST: 2

Defocus amount in forming the first modified layer R1: 30 μm

Defocus amount in forming the second modified layer R2: 20 μm

According to the optical device manufacturing method in this preferredembodiment, the plural concave portions 25 and the plural convexportions 26 can be alternately formed along the thickness of the opticaldevice wafer W even in the case that the thickness of the wafer W issmall. Further, the plural modified layers R juxtaposed along thethickness of the wafer W are staggered in the direction along the widthof each division line ST in the modified layer forming step.Accordingly, the wafer W can be divided so as to form a corrugated shapealong the thickness of the wafer W by simply applying an external forceto the wafer W in the dividing step. As a result, complication of eachstep and elongation of the time of each step can be suppressed tothereby effect efficient manufacture of the optical devices 1.

The present invention is not limited to the above preferred embodiment,but various modifications may be made. The size, shape, etc. of theparts in the above preferred embodiment shown in the attached drawingsare merely illustrative and they may be suitably changed within thescope where the effect of the present invention can be exhibited.Further, the above preferred embodiment may be suitably modified withoutdeparting from the scope of the object of the present invention.

For example, while the dividing step is performed by using a breakingapparatus in the above preferred embodiment, the dividing step in theabove preferred embodiment may be performed by using any apparatuscapable of dividing the optical device wafer W along the division linesST to obtain the individual optical devices 1.

Further, the steps of the optical device manufacturing method in theabove preferred embodiment may be performed by using separateapparatuses or by using the same apparatus.

The present invention is not limited to the details of the abovedescribed preferred embodiment. The scope of the invention is defined bythe appended claims and all changes and modifications as fall within theequivalence of the scope of the claims are therefore to be embraced bythe invention.

What is claimed is:
 1. An optical device comprising: a substrate formedof a light transmitting material; and a light emitting layer formed on afront surface of said substrate; both the front surface and a backsurface of said substrate being parallel to each other and havingsubstantially the same rectangular shape; said substrate having fourside surfaces connecting the front surface and the back surface of saidsubstrate; each side surface of said substrate having a corrugatedsectional shape such that a plurality of concave portions and convexportions are alternately formed.
 2. A manufacturing method for opticaldevices each including a substrate formed of a light transmittingmaterial and a light emitting layer formed on a front surface of saidsubstrate, both the front surface and a back surface of said substratebeing parallel to each other and having substantially the samerectangular shape, said substrate having four side surfaces connectingthe front surface and the back surface of said substrate, each sidesurface of said substrate having a corrugated sectional shape such thata plurality of concave portions and convex portions are alternatelyformed, said manufacturing method comprising: an attaching step ofattaching a protective tape to a front side of an optical device waferhaving a light emitting layer on the front side, said light emittinglayer of said optical device wafer being partitioned by a plurality ofcrossing division lines to define a plurality of separate regions wheresaid optical devices are respectively formed; a modified layer formingstep of applying a laser beam having a transmission wavelength to saidoptical device wafer along each division line from a back side of saidoptical device wafer after performing said attaching step, in acondition where the focal point of said laser beam is adjusted insidesaid optical device wafer so as to be stepwise shifted along thethickness of said optical device wafer from the front side to the backside thereof, thereby forming a plurality of modified layers juxtaposedin the direction along the thickness of said optical device wafer; and adividing step of applying an external force to said optical device waferafter performing said modified layer forming step, thereby dividing saidoptical device wafer along each division line to obtain said individualoptical devices; said plurality of modified layers juxtaposed in thedirection along the thickness of said optical device wafer beingstaggered in the direction along the width of each division line in saidmodified layer forming step; a crack being formed between any adjacentones of said plural modified layers juxtaposed along the thickness ofsaid optical device wafer and staggered along the width of each divisionline in said dividing step, thereby dividing said optical device waferalong each division line so as to form a corrugated sectional shapecorresponding to the shape of each side surface of said substrate ofeach optical device.